Magnetron Sputtering Of Graphite Research Articles

Preparation of nickel-containing conductive amorphous carbon films by magnetron sputtering with negative high-voltage pulsed substrate bias

Nickel-containing amorphous carbon (a-C-Ni) films were deposited by magnetron sputtering of graphite and nickel. Graphite magnetron sputtering power was 1500 W. Nickel magnetron sputtering power changed from 0 W to 1000 W, allowing control of the Ni concentration in the films from 0 to 58 at.%. Growth rates of a-C-Ni films were 1.4–2.5 μm/h. High-voltage negative pulsed bias voltage of ‐3 kV amplitude, frequency of 1 kHz, and pulse duration of 50–250 μs was applied to a substrate. The chemical composition of the films was determined using Auger electron spectroscopy. The surface morphology was observed by atomic force microscopy (AFM). The film structure was characterized by Raman spectroscopy and X-ray diffractometry (XRD). The resistivity of the films was measured by a four-point probe method. Film properties that are changed by the added metal, such as structure, electrical resistivity, and hardness, were evaluated and compared with those of pure a-C films as well as with literature values for a-C-Ni films. It is shown that the resistivity of a-C films depends on the duration of the bias voltage pulses and varies from 3.4 to 7.6·10−2 Ohm·cm at pulse duration 50 and 250 μs, respectively. In the case of Ni doping, the a-C-Ni film resistivity can be reduced to 6.7·10−4 Ohm·cm. Where Ni is included in the film in the form of Ni3C carbide, which has hexagonal (hcp) modification, the crystallite size averages 12 nm. The film has a columnar structure and carbon is also present as a graphite-like interlayer 3 nm thick between the Ni3C crystallites. At sputtering power of 600 W of nickel magnetron, a-C-Ni film with resistivity of 5.3·10−3 Ohm·cm is obtained, which can be used as a barrier layer in thermoelements based on bismuth telluride.

Bias voltage dependence of superlubricity lifetime of hydrogenated amorphous carbon films in high vacuum

Abstract We deposit hydrogenated amorphous carbon (a-C:H) films by magnetron sputtering of graphite in an Ar + C 2 H 2 mixture at various bias voltages. The mechanical properties, Raman spectra, and high-vacuum frictional behaviors of the a-C:H films indicate that the films deposited at bias 0, –50, and −100 V are polymer-like carbon (PLC) films and the film deposited at −150 V is a diamond-like carbon (DLC) film. The lifetimes of superlubricity, with friction coefficient ∼0.002, of the PLC films in high-vacuum increase from 10000 to 28000 cycles with increasing bias, although the film thicknesses decrease. The DLC film's wear-life is ∼600 cycles. The enhanced wear-resistance in PLC films is attributed to improvement of the crosslinking degree of the PLC network and the film compactness.

Pulsed magnetron sputtering and ion-induced annealing of carbon films

Thin carbon films are deposited on a silicon substrate at room temperatures via the biased pulsed magnetron sputtering of graphite in the physical (Ar, Kr, Xe) and reactive (Ar: CH4) modes at a different sputtering power density varying from 40 to 550 W/cm2. To ensure ion-assistance, negative bias of the substrate is set during film deposition by means of both DC and pulsed power sources. Some deposition parameters lead to a high hardness of the films (12.5 GPa), optical transparency, a surface resistance of RS > 109 Ω/h, and developed nanomorphology of the sample surface which bears visible inclusions with a lateral size of 35 nm. Some of the films are annealed after deposition with a C+-ion beam with an energy of 20 keV. A correlation between the parameters of magnetron deposition and ion-beam modification and the examined characteristics of the films is found. Different R S values in a wide range can be achieved by means of simple adjustment of the parameters and modes during magnetron sputtering and ion-beam modification.

Titanium Carbide Obtained by Magnetron Sputtering of Graphite on Heated Titanium Substrate

Titanium Carbide Obtained by Magnetron Sputtering of Graphite on Heated Titanium Substrate

Solid nanocrystalline fullerite-containing carbon coatings

Solid carbon coatings with a high content of nanocrystalline fullerite have been obtained using unbalanced magnetron sputtering of graphite under conditions of pulsed high-voltage ion bombardment of the film growing on a substrate. It is established that samples possessing the maximum hardness (18.8 GPa) are characterized by maximum values of the volume fraction of fullerite in the coating (50%), coherent scattering domain size (53 nm), degree of preferred grain orientation (85%), relative deformation of the lattice (1.02%), and internal compressive stresses (2.91 GPa). The observed behavior is consistent with the mechanism of strengthening that accounts for the phenomenon of superhardness in nanocrystalline and nanocomposite materials. This assumption is confirmed by the results of investigation of the morphology of growing coatings.

Degradation of a C/CrC PVD coating after annealing in Ar+H2 at 700°C studied by Raman spectroscopy and transmission electron microscopy

The thermal stability of a hydrogen free C/CrC coating was the focus of this study. The coating was deposited by unbalanced magnetron sputtering of graphite and Cr metal targets in a non-reactive argon atmosphere at high ion irradiation conditions. The coating possessed a nanocomposite structure with amorphous carbon embedded in a metastable NaCl (B1) structure CrC matrix. The nanometre amorphous carbon clusters formed layers within the CrC matrix, producing a self-assembled multilayer structure. In this paper, degradation of the multilayer nanocomposite structure and NaCl (B1) structure CrC phase was evaluated by annealing at 700°C in Ar+5%H2 atmosphere for 30 minutes. Microstructures of the as-deposited and annealed coating were characterised using Raman spectroscopy and cross-sectional transmission electron microscopy (TEM) coupled with electron energy filtered mapping. Raman spectroscopy suggested the presence of graphitic carbon in the coating after annealing, together with a trace of Cr2O3 associated with coating growth defects. TEM investigation of the cross sections of annealed coating revealed regions of C enrichment at the very top (∼40 nm) and bottom (∼10 nm) of the coating, which was confirmed by Raman spectroscopy. However, the central region of the coating retained its composite C/CrC multilayer structure. Tentative mechanisms of C enrichment are proposed. The advantages and limitations of Raman spectroscopy and TEM techniques in studying C/CrC coating are also discussed.

Spectral ellipsometry of amorphous hydrogenated carbon grown by magnetron sputtering of graphite

Polarization angles for films of amorphous hydrogenated carbon produced by magnetron sputtering of graphite in argon-hydrogen plasma have been measured using spectral ellipsometry (in the range of photon energies 1–5 eV). The dispersion of the imaginary and real parts of the permittivity has been reconstructed. It is shown that the data obtained are consistent with the Kramers-Kronig formalism in the frequency range under study. The sum rule allowed us to conclude that the density of states is nonuniformly distributed over energies and to reveal the characteristic threshold energies in the spectrum of the effective density of states (2 and 3.8 eV). The possibility of describing the energy spectrum of electrons using Gaussian curves is shown. The features of the energy distribution of states are attributed to the contribution of the σ and π states.

Superelastic Fullerene-like Carbon Nitride Coatings Synthesised By Reactive Unbalanced Sputtering Magnetron

The present paper presents the results of in depth process characterisation and microstructural investigation of fullerene-like carbon nitride (FL - CNx) coatings combined with deformation analysis, such as indentation testing, in order to assess its performance. Unbalanced reactive magnetron sputtering of graphite in a nitrogen containing atmosphere is essential for the growth of FL - CNx structures due to CxNy molecules, which are preformed in the process and may act as precursors or growth templates. The deposition process is best described as a hybrid of plasma vapour deposition and chemical vapour deposition. The fullerene-like (FL) structure leads to extraordinary mechanical properties which are assessed by nanoindentation. It exhibits a low work of indentation (usually a property associated with superhard materials) and also a low to moderate resistance to penetration. Therefore, deformation energy is predominantly stored elastically and released after unload giving it a tough and resilient character. In addition, the relatively low modulus leads to a spreading of the contact stresses over a larger volume and consequently to low stress gradients at the substrate/film interface. This hinders substrate/film delamination under load and therefore results in a high load bearing capability, while the coating asperities behave elastically with no tendency to brittle fracture in tribological contact. This characteristic combined with the low coefficient of friction reveals a coating which may be suitable for many tribological applications.

Scanning tunneling spectroscopy of a-C:H and a-C:(H, Cu) films prepared by magnetron sputtering

Scanning tunneling spectroscopy was used to study a-C:H and a-C:(H, Cu) films under atmospheric conditions; these films were formed on semiconductor (Si) and metallic (Cr/Si) substrates using dc magnetron sputtering of graphite or graphite/copper targets. The local density of electron states was determined from normalized differential tunneling conductance with the aim of probing the individual sp 2-phase clusters. The well-defined valence-band edge and the varying (i.e., dependent on the scanning coordinate) shape of the distribution of the density of electron states within the conduction band are characteristic of the a-C:H films; also, the largest experimental value of the band gap in these films is ∼3 eV; finally, the tendency towards the stable position of the Fermi level at a level of ∼1 eV above the valence-band top is observed in a-C:H films. The a-C:(H, Cu) films are homogeneous with respect to the local density of electron states, which is accounted for by the formation of a homogeneous surface layer in the course of growth.

Laboratory study of the transport and condensation of hydrocarbon radicals and its consequences for mitigating the tritium inventory in the ITER-FEAT divertor

The surface loss probability β of CH 3 radicals at a-C:H surfaces has been determined by analysis of the carbon deposition profiles along a tube flow reactor directly coupled with a methane RF discharge. β is equal to (1.0±0.2)×10 −3 for a methyl to atomic hydrogen flux ratio of 10:1. β remains the same in the temperature range 300–800 K and decreases slightly between 800 and 1200 K. The deposition rate drops drastically in the range 400–800 K. Above 800 K the carbon deposition is regained. From separate experiments on magnetron sputtering of graphite by D ions, it is inferred that at 300 and 900 kinetic CH x species react at the C:D surface with the same probability. In contrast, the deposition of thermal C x H y radicals decreases by a factor of 25 with a temperature rise from 320 to 400 K, remaining at this low level up to 1000 K. The implications of these results for co-deposition in the ITER-FEAT divertor are discussed.

Optical properties of amorphous carbon films deposited by magnetron sputtering of graphite

The thermal stability of amorphous carbon (a-C and a-C:H) has been studied by ellipsometry and spectrophotometry in the visible and near-UV range (1.5–5.6 eV). The dielectric function of amorphous carbon has been derived and analyzed using the Kramers-Kronig technique. The conventional analytical approach is shown to be insufficient for the analysis of thermally treated samples. The fundamental absorption edge is analyzed with respect to collective effects in nanoscale fragments of the graphite-like component of the amorphous carbon structure. Two types of graphite-like clusters contributing to the spectral dependence of the fundamental absorption edge and modified by thermal treatment are revealed.

Comparison of composition and bonding states of constituents in CNx layers prepared by d.c. plasma and magnetron sputtering

Layers of CNx were grown on polished Si(100) wafers and cleaved NaCl(100) substrates by reactive sputtering of graphite in d.c. nitrogen plasma and also by d.c. or r.f. magnetron sputtering of graphite in N2. The deposited layers were studied in situ by XPS and ex situ by Fourier transform infrared spectroscopy (FTIR). Direct current plasma deposition resulted in brown transparent layers of high nitrogen content, close to CN with 1 : 1 stoichiometry, as determined by XPS. Direct current magnetron sputtering resulted in layers with slightly lower nitrogen content. The grey opaque CNx layers deposited by r.f. magnetron sputtering contained only 33–38 at.% N. The broad C 1s and N 1s lines manifested several bonding states. The relative intensities of the component peaks varied with the preparation conditions. Differences were observed also in the 1000–1700 cm−1 region of the FTIR spectra. Assignments of the various photoelectron peak components were proposed, based on published results and measurements on model compounds and binding energy separations between the related C 1s and N 1s lines. It was deduced that the concentration ratio of sp3-type C–N clusters to that of the sp2-type clusters was significantly higher for the r.f. magnetron-sputtered layers than for the d.c. plasma-deposited layers. The observed differences can be explained by the specificity of unbalanced magnetron sputtering, providing an increased amount of plasma ions and intensive bombardment of the as-deposited material at the growing surface. The increase of the ratio of sp3-type C–N clusters to the sp2-type C N clusters can be enhanced further for the r.f. magnetron-sputtered samples by applying a negative bias to the substrate. Copyright © 2000 John Wiley & Sons, Ltd.

Plasma substrate interaction effects on composition and chemical structure of reactively r.f. magnetron sputtered carbon nitride films

During variable unbalanced r.f. magnetron sputtering of graphite in a 70/30 N 2/He atmosphere the neutral and ionic particle fluxes on the substrate were analyzed for various discharge conditions using energy-resolved mass spectrometry and probe measurements. These data were related to the chemical composition, bonding structure and Young's modulus of the deposited CN x films. The magnetron discharge was found to produce an unexpectedly high concentration of N atoms being the predominant nitrogen precursors for the carbon nitride formation. Depending on r.f. power density and discharge pressure, the arriving fluxes of N and C atoms range from 3×10 16 to 6×10 18 cm −2 s −1 and from 1×10 15 to about 8×10 15 cm −2 s −1, respectively, while the ionic fluxes of nitrogen and carbon were measured to be two orders of magnitude lower. The energy flux density of the ion bombardment varies from 5×10 −4 to 2×10 −1 W/cm 2 over the range of discharge conditions. The overall chemical composition of the CN x films is primarily governed by the flux ratio of N to C atoms. For low Φ N/Φ C ratios, N atoms are incorporated up to 25 at.% as substitutions of C atoms in aromatic clusters of a sp 2/sp 3 hybridized carbon matrix. With increasing arrival flux ratio the excess of N atoms is additionally bonded in linear CN structures terminated with H atoms when hydrogen is present in the discharge. An intensive for bombardment results in a reduced N concentration of the films due to an enhanced desorption of N atoms from the growing surface, mainly, however, in changing the film structure from graphite-like to amorphous. Caused by these structural changes, the Young's modulus of the CN x films decreases from about 110 to 55 GPa.

The kinetics of sputtered deposited carbon on silicon: a phenomenological model

A phenomenological model based on the rate equations for the carbon sputter deposition on Si surface is proposed. The processes of carbon adsorption, formation of SiC and transition from sp 2 to sp 3 sites induced by low energy ion bombardment are included. The calibration of the model was performed with the experimental results. The amorphous carbon films were deposited by magnetron sputtering of graphite with Ar + ions. The energy of ions bombarding the growing film was varied by applying a bias voltage on the substrate. It is shown that the non-monotonous kinetics of film growth is determined by the variations of surface composition at different stages of growth.

The unique capability of X-ray photon spectroscopy and X-ray excited Auger electron spectroscopy in identifying the sp2/sp3 ratio on the surface of growing carbon films

Abstract The C KVV Auger spectra of polymers: polyethylene (sp3), p-quaterphenyl (sp2) and polystyrene (sp2/sp3=3/1) have been studied. The possibility for a synthesis of Auger spectrum for polystyrene by that for p-quaterphenyl (three parts) and polyethylene (one part) is shown. A combination of X-ray photon spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) data were used for study a chemical states of carbon atoms on glassy carbon surface before (GC1) and after (GC2) scratching. A magnetron sputtering of graphite in the gas mixtures Ar+C6H12, Ar+CF4 and Ar+O2 have been investigated ex situ by XPS and XAES. The formation and relative concentrations of C–O, CO; and C–F, C–F2 bonds for sputtering in Ar+O2 and Ar+CF4 mixtures, respectively, has been determined by XPS. The transition of carbon atoms from the sp2-bonding to the sp3-hybridized state has been observed by XPS and XAES.

Reactively r.f. magnetron sputtered carbon nitride films

Carbon nitride films have been prepared on silicon (100) substrates by reactive r.f. magnetron sputtering of graphite in pure nitrogen to investigate the influence of the ion bombardment on film characteristics. Deposition was carried out at frequencies of 4.00 MHz and 13.56 MHz, respectively, for various discharge conditions in the r.f. power range between 50 W and 1000 W at process gas pressures of 0.3 Pa to 8 Pa and at substrate temperatures up to 500°C. The films were analyzed as to their bonding structure, chemical composition, density and Young's modulus using Fourier transform IR and Raman spectroscopy, electron probe microanalysis and elastic recoil detection analysis. X-ray diffraction and analysis of ultrasonic surface waves. The results indicate that both the energy flux density of the ion bombardment and the bombardment energy per condensing atom of carbon and nitrogen are fundamental internal process parameters for carbon nitride formation. The discharge frequency did not have a remarkable influence on the film features. All CN x films deposited in this way are found to be amorphous. At increasing energy flux density the bonding structure was found to change from a more graphite-like structure with mainly C≡N triple bonds to a more disordered sp 2 bonded carbon phase with predominantly C=N double bonds incorporated. The overall N/C concentration ratio of the films has a maximum of about 1.0 at the lowest energy flux density of the ion bombardment and runs through a minimum of below 0.4 with increasing energy flux density attended by increasing Young's moduli of the carbon nitride films. This is attributed to desorption of volatile species and nitrogen atoms from the surface region of the films. The density of the films increases with the bombardment energy per condensing atom of carbon and nitrogen, but remains below that of graphite.

Ion bombardment diagnostics in a nitrogen RF magnetron sputtering discharge

Abstract The identity, fluxes and kinetic energy distributions of positive ions bombarding the substrate during radio frequency (RF) magnetron sputtering of graphite in a balanced nitrogen plasma have been investigated for various settings of discharge power and pressure by using energy-mass spectrometry analysis and probe measurements. Three prominent groups of ionic species were identified to form the ion bombardment. The first is due to the process gas ions, of which the primary ions of nitrogen are the dominant ones. The two further ionic groups are clearly related to sputtered carbon and its reaction products with nitrogen. The net fluxes of these ionic species respond very sensitively to changes in the discharge conditions. The ratios of the net ion fluxes of C + and N + to their atom deposition rates indicate that nearly all carbon species for film growth arise from the arriving flux of sputtered C atoms, whereas the bombarding N + flux acts as an intense nitrogen source for the film chemistry. The ion kinetic energy distributions measured for predominant ions, such as C + , N + , N + 2 and (CN) + 2 , were observed to be qualitatively similar in their shapes and trends, clearly reflecting the ions' sensitivity to RF modulations and to collision processes while passing the near-substrate sheath. Over the range of power and pressure, the mean kinetic energy of the bombarding ions was from about 25 eV to 45 eV. With the found data, the energy flux density of the ion bombardment and the averaged bombardment energy per condensing carbon and nitrogen atom were calculated, these being fundamental internal process parameters for judging the effect of the bombarding ion flux on carbon nitride formation.

Tribological study of CN x films prepared by reactive d.c. magnetron sputtering

The effects of both substrate bias voltage during fabrication and countersurface materials during sliding, on the tribology of CN, films are reported. Amorphous CN, films (12–24 at.% N), about 1 μm thick, were deposited onto Si(100) substrates at 600°C by d.c. magnetron sputtering of graphite in a nitrogen plasma. Tribological behaviour of the CN x films was evaluated in continuous, unidirectional sliding against different materials (Al 2O 3, 52100 steel, and diamond film-coated Si 3N 4 balls) in pin-on-disk tests. Low friction coefficient values (μ = 0.1–0.25) were found for soft, but rougher, films prepared at lower bias voltage (−300 V). Such films exhibited a relatively high wear rate (≥ 1.3 × 10 −13m 3N −1m −1), partial transfer to the alumina ball, but the wear debris acted as a lubricant during sliding. Harder CN x films prepared at higher bias voltage (−700 V) resulted in lower wear but higher friction levels (μ = 0.25–0.5) when sliding against alumina. The hardest film (23 GPa) prepared at a pressure of 0.5 Pa also showed lower wear, but relatively high and variable friction, behaviour when sliding against 52100 steel (μ = 0.4–0.5). Sliding against the rough, polycrystalline diamond coated countersurface eventually led to film delamination. Friction coefficients calculated from scratch test measurements are also compared with previous results obtained for diamond-like carbon films.

Plasma diagnostic studies to the carbon nitride film deposition by reactive r.f. magnetron sputtering

During r.f. magnetron sputtering of graphite in pure nitrogen the near-substrate plasma has been systematically investigated as to the ionic species and their fluxes on the substrate for various discharge conditions using energy-resolved mass spectrometry in conjunction with probe measurements. These data were related to the chemical composition, bonding structure and internal stress of the deposited carbon nitride films which had been studied by several analytical methods. Besides the process gas ions at which N 2 + and N + are the dominant ones, the r.f. sputter plasma is rich in ionic carbon C i + ( i = 1–5) and ionized groups of C i N j + ( j = 1,2) together bombarding the growing film. The relative net fluxes of these ionic species are strongly dependent on discharge conditions. The total flux was found to be from close to 4 × 10 14 cm −2 s −1 to about 6 × 10 15 cm −2 s −, comparable to the rate of deposited carbon and nitrogen atoms. The mean impact energy of the bombarding ions varies from about 25 eV to 45 eV. The higher values of flux and energy were at high r.f. power and low pressure. The results of the film analyses show that both the power density supplied to the substrate by the ion bombardment and the bombardment energy per condensing atom of carbon and nitrogen are fundamental process parameters of the carbon nitride formation. These parameters were calculated to range from 2 × 10 −3 W cm −2 to about 45 × 10 −3 W cm −2 and from 5 eV to 35 eV, respectively. The overall N/C ratio of the films has a maximum of 0.9 achieved at the lowest power density and runs through a minimum of below 0.4 with increasing power supply to the substrate attributed to desorption of volatile species in this range of power. At increasing ion bombardment energy per deposited carbon and nitrogen atom the bonding structure was found to change from a mixture of graphitic and disordered sp 2-bonded carbon with mainly CN triple bonds to a more disordered phase with predominantly CN double bonds incorporated; this was attended by increasing compressive residual stress within the carbon nitride films. These results may be of importance in finding a way to produce carbon nitride with definite phase by r.f. magnetron sputtering.

Photoluminescence fatigue in amorphous carbon ( a-C) films prepared by d.c. magnetron sputtering

We have studied the fatigue effect in unhydrogenated amorphous carbon ( a-C) films prepared by d.c. magnetron sputtering of graphite. At 12 K the fatifued photoluminescence spectra show neither a spectral shape change nor peak shift during illumination. The fatigued photoluminescence intensity at a fixed energy shows a t − b time process during illumination. The self-recovery of the fatigued photoluminescence in the dark requires much more time than hydrogenated amorphous silicon ( a-Si : H) and less than amorphous phosphorus ( a-P). The light induced defects in a-C films are in metastable states and explained to be π defects rather than dangling bonds (σ defects) as in a-Si : H or hydrogenated amorphous carbon ( a-C : H).